In the processing and recovery of waste materials it has become well known that mixed waste materials may be conveniently separated into light and heavy materials by a rotary drum through which a stream of air is made to flow at high velocity. A suitable conveyor penetrates into one end of the drum and deposits the mixed materials in a suitable location within the drum. The drum is made to rotate about a longitudinal axis which is disposed at a selected angle to the horizontal. Thus, the mixed materials will be lifted and dropped within the drum as it is rotated.
During such agitation of the materials within the drum, it has been found that light materials will be entrained within the air stream and will be carried out the upper end of the drum for further processing, use or disposal. The heavy materials will be moved progressively downwardly in the drum and will eventually fall out the lower end of the drum.
It has been found that the ratio of lights-to-heavies may be regulated by controlling the angle of inclination of the drum and consequently varying the velocity of the air stream flowing through the drum. Therefore, there is provided means for raising and lowering one end of the drum so as to change its angle of inclination as desired. Usually this is done by raising or dropping the lower end since the upper end is desirably retained in a predetermined relationship with other processing apparatus. Therefore, the lower end of the drum, that end from which heavy materials are allowed to drop, is raised or lowered to adjust the drum to a selected angle of inclination, and thus the drum is moved about an axis at or adjacent its upper end from which light materials are extracted by the air stream.
A primary conveyor, preferably a trough-shaped belt conveyor, is usually disposed beneath the lower end of the drum in order to receive and carry away the heavy materials dropping from the drum. It will be apparent that if the drum is inclined to a relatively extreme angle of inclination from the horizontal, the distance from the primary conveyor to the drum may be relatively short. Therefore, the heavy materials will fall a short distance to the conveyor with relatively low impact thereon. However, as the end of the drum is raised toward the horizontal, the distance between it and the conveyor increases. Accordingly, when the drum is in one of its higher positions, the heavy materials are required to fall a considerable distance, sometimes a distance of several feet when large drums are used. It will be apparent that in such cases the heavy materials will impact very heavily upon the conveyor, possibly causing damage to it. In some cases also the materials might actually miss engagement with the conveyor altogether.